Preheat the oven to 350°F.
Heat the oil over medium heat in a saucepan. Add the onions and parsley. Cover and cook for 4 to 5 minutes over low heat. Remove the lid. Pour the vinegar over the onions and let it evaporate for 2 to 3 minutes. Add the cabbage and potatoes. Season with salt and pepper, cover, and cook over medium heat for 30 minutes, stirring occasionally. Add the sausages and syrup, and cover. Cook in the oven for 45 minutes. Serve with Dijon mustard and cold beer.